The present invention relates to a projection type display apparatus wherein an optical image formed on an image display element is projected on a larger scale onto a screw through a projection lens.
Heretofore, a projection type display apparatus for projecting an optical image formed on an image display element onto a screen or the like has been known and used practically. A liquid crystal panel or the like has recently been utilized as the image display element. To provide a brighter image, a technique of using plural light sources to improve the brightness is disclosed in JP-A-8-036180.
FIG. 7 illustrates a conventional optical unit. The optical unit includes a light source 51, a paraboloidal reflector 57, light transfer means 52, an image display element 53, a projection lens 54, and a UV-IR filter 55. The light source 51 emits light. The paraboloidal reflector 57 reflects light emitted from the light source 51. The light transfer means 52 irradiates an image display element 53 with light after emission and reflection from the light source 51 and the paraboloidal reflector 57. The image display element 53 forms an optical image. The projection lens 54 projects the optical image provided from the image display element 53 onto a screen (not shown). The UV-IR filter 55 cuts off ultraviolet and infrared rays would otherwise cause deterioration of optical elements.
First lenses 52a1 and 52a2 of the light transfer means 52 condense light emitted from light sources 511 and 512 to second lenses 52b1 and 52b2 to form light-source images in the vicinity of the second lenses 52b1 and 52b2. Light which has passed through the second lens 52b is condensed by an optical coupling lens 52c and is incident on a third lens 52d whose light ray angle is adjusted. The resulting light is then incident on the image display element 53.
In the optical unit shown in FIG. 7, the light emitted from the light source 51 is condensed at least twice by the second lens 52b and the third lens 52d, so that the optical path length thereof becomes long, giving rise to the problem of increase in size of the optical unit. Moreover, since the number of optical parts used is large, there arises the problem that the cost of the optical unit is high.
In FIG. 7, for example if a point light source not having a finite shape is disposed at a focal point of the paraboloidal reflector and emits light, the light emitted from the light source is reflected by the paraboloidal reflector and thereafter travels approximately in parallel. However, the light source 51 has a finite size and therefore, for example, light emitted from a position deviated from a focal point in the light source 511 is not collimated but generates aberration, as indicated by a dotted line 60. As a result, for example, the light may directly enter the optical coupling lens 52c without being incident on the second lens 52b1 or may become incident on the second lens 52b2. Thus it becomes impossible to let light be incident on the image display element 53.
The present invention has been accomplished in view of the above-mentioned problems, and it is an object of the invention to provide a projection type display apparatus or an optical unit capable of attaining the reduction of cost by minimizing the number of optical parts and also capable of attaining a high luminance by irradiating an image display element with light emitted from a light source without leakage.